1. Field of the Invention
The present invention relates to a method of forming a conductive pattern and in particular a conductive pattern where vertical leads are formed as external connection terminals of a magnetic head.
2. Related Art
On a thin-film magnetic head used in a magnetic disk apparatus, so-called “vertical leads” formed in the shape of columns that extend perpendicular to a thin magnetic film and pass through an alumina protective film provided on an outer surface of the magnetic head are used as terminals for electrically connecting to external devices.
A typical thin-film magnetic head is provided with two read vertical leads and two write vertical leads, making a total of four vertical leads.
However, the miniaturization of thin-film magnetic heads in recent years has made it increasingly necessary to form the vertical leads with narrow widths so that a plurality of vertical leads can be provided in a narrow space.
In particular, when using DFH (Dynamic Flying Height) technology where a heater is incorporated in a magnetic head to control the float height of the magnetic head above a magnetic medium, in addition to the four read and write vertical leads, it is necessary to provide a further two vertical leads to connect the heater. Therefore, out of the limitations for suppressing the size of the magnetic head, it is necessary to make the widths of the vertical leads even smaller.
To ensure that the magnetic head has sufficient mechanical strength, the alumina protective film cannot be made very thin. This means that the heights of the vertical leads cannot be greatly reduced.
That is, in recent years, there has been increasing demand for the vertical leads to be formed with narrower widths but with no reduction in height.
For example, there is demand for vertical leads where the width is around 30 to 40 μm and the height of the vertical leads that is substantially equal to the thickness of the alumina protective film is around 70 to 80 μm.
The vertical leads of a magnetic head are normally formed using photolithography. That is, a photosensitive resist layer is formed on a surface of the magnetic head on which the vertical leads are to be formed and then the photosensitive resist layer is exposed and developed so as to remove the photosensitive resist layer only at the formation positions of the vertical leads. After this, a conductive pattern that serves as the vertical leads is formed by plating, for example, at the parts where the photosensitive resist layer has been removed.
However, during photolithography, it is difficult to expose and develop the photosensitive resist layer in a suitable manner for vertical leads such as those described above where the aspect ratio of the height to the width is high.
A technique for exposing and developing a photosensitive resist layer corresponding to vertical leads where the aspect ratio of the height to the width is high is disclosed in Patent Document 1.
Patent Document 1 discloses a technique for forming the photosensitive resist layer so that vertical leads where the aspect ratio of the height to the width is high can be produced by repeatedly carrying out an exposing/developing process at parts of the photosensitive resist layer that correspond to the vertical leads.
Patent Document 1
Japanese Laid-Open Patent Publication No. H07-272216
However, with the method of forming the vertical leads of a magnetic head disclosed in Patent Document 1, even if it is possible to form a suitable photosensitive resist layer for vertical leads with a high aspect ratio, there is the problem that it will still be difficult to form the vertical leads by plating.
That is, with the technique disclosed in Patent Document 1, even if the photosensitive resist layer can be suitably exposed and developed for the formation of vertical leads with widths of around 30 to 40 μm and heights of around 70 to 80 μm, for example, it is difficult for plating solution to spread inside holes of such shapes, and therefore it is extremely difficult to form a conductive pattern (i.e., vertical leads) with favorable electrical connectivity inside such holes.